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Abstract

Introduction

Dehydration and malnutrition commonly occur together among ill children in developing
countries. Dehydration (change in total body water) is known to alter weight. Although
muscle tissue has high water content, it is not known whether mid-upper arm circumference
(MUAC) may be altered by changes in tissue hydration. We aimed to determine whether
rehydration alters MUAC, MUAC Z score (MUACz), weight-for-length Z-score (WFLz) and
classification of nutritional status among hospitalised Kenyan children admitted with
signs of dehydration.

Study procedure

We enrolled children aged from 3 months to 5 years admitted to a rural Kenyan district
hospital with clinical signs compatible with dehydration, and without kwashiorkor.
Anthropometric measurements were taken at admission and repeated after 48 hours of
treatment, which included rehydration by WHO protocols. Changes in weight observed
during this period were considered to be due to changes in hydration status.

Results

Among 325 children (median age 11 months) the median weight gain (rehydration) after
48 hours was 0.21 kg, (an increase of 2.9% of admission body weight). Each 1% change
in weight was associated with a 0.40 mm (95% CI: 0.30 to 0.44 mm, p < 0.001) change
in MUAC, 0.035z (95% CI: 0.027 to 0.043z, P < 0.001) change in MUACz score and 0.115z
(95% CI: 0.114 to 0.116 z, p < 0.001) change in WFLz. Among children aged 6 months
or more with signs of dehydration at admission who were classified as having severe
acute malnutrition (SAM) at admission by WFLz <-3 or MUAC <115 mm, 21% and 19% of
children respectively were above these cut offs after 48 hours.

Conclusion

MUAC is less affected by dehydration than WFLz and is therefore more suitable for
nutritional assessment of ill children. However, both WFLz and MUAC misclassify SAM
among dehydrated children. Nutritional status should be re-evaluated following rehydration,
and management adjusted accordingly.

Keywords:

Introduction

Malnutrition is a leading cause of death among children under 5 years in sub-Saharan
Africa [1]. Two forms of severe acute malnutrition (SAM) are recognized: severe wasting and
kwashiorkor. The principle diagnostic criteria for SAM are based on weight for length
Z score (WFLz) [2] and mid-upper arm circumference (MUAC) [3-6].

Dehydration due to gastroenteritis and other illnesses is common amongst children
admitted to hospital in sub-Saharan Africa [7]. Diarrhoea and acute malnutrition often occur simultaneously [8]. In most clinical guidelines, dehydration is assessed by percent change in weight.
Severe dehydration is commonly regarded as a weight change of more than 10% [9]. Hydration status and the contents of the gastrointestinal tract may cause short
term variation in weight, due to changes in total body water, thus WFLz can be influenced
by hydration status in sick children.

MUAC measures the circumference of the upper arm which is made up of lean muscle,
fat tissue, [4] as well as a cross section of bone and blood vessels. MUAC is therefore a proxy measure
of protein and lipid reserves. Lean muscle tissue contains about 75% water and therefore
MUAC could conceivably be affected by tissue dehydration. However, this has not been
established.

Among clinical signs of dehydration, three (prolonged capillary refill time, abnormal
skin turgor and abnormal respiratory pattern) are regarded as the most reliable in
diagnosing dehydration [10]. Current WHO guidelines, classify children as having severe, 'some' or 'no' dehydration,
using signs including unconsciousness/lethargy/restlessness, sunken eyes, inability
to drink, thirst, abnormal skin turgor [9]. Some of these signs, such as sunken eyes and abnormal skin turgor may also occur
as features of acute wasting.

We aimed to determine whether rehydration alters MUAC and WFLz among children admitted
to hospital with signs compatible with dehydration, and evaluate the potential for
misclassification of nutritional status.

Methods

Study location

The study was conducted from February 2009 through August 2009 at Kilifi District
Hospital, located in a rural area at the Kenyan Coast, approximately 65 kilometres
north of Mombasa. Kilifi is the second poorest district in Kenya with 67% of the population
living in poverty [11]. Under nutrition is endemic with 25% of the children under five underweight (WFAz
<-2)[12] and hospital records indicate that approximately 500 cases of severe acute malnutrition
admitted at the hospital every year, about 20% of whom are HIV exposed or infected.

Study design

Using a before-after study design, anthropometric measurements were taken first at
admission (before the hydration therapy) and again at 48 hours after admission.

Study participants

We recruited children admitted to the hospital aged between 3 months and 5 years with
one or more of the following clinical signs of dehydration at admission: reduced skin
turgor, sunken eyes, delayed capillary refill (>3 seconds), weak pulse, deep breathing,
or a palpable limb temperature gradient [9]. At admission, the admitting clinician assessed the clinical signs and described
the initial diagnosis of the children. Age was ascertained through individual health
cards or previous hospital records. Clinical details of all patients admitted were
immediately recorded onto a database. Eligible patients were automatically flagged
by this system, based on the inclusion criteria. These children were identified and
their MUAC, weight and height were measured and recorded. Measures were repeated after
48 hours. Rehydration and other care were provided by experienced research clinicians
not directly involved in this study. Management, following the current WHO guidelines,
included special fluids, feeds and procedures for SAM [9]. Children were excluded from the study if they had kwashiorkor (bipedal oedema with
or without dermatosis, a protruding belly or hair changes) since short-term changes
in weight may be due to changes in oedema, or if they died or were discharged before
the second set of measurements.

Study Procedures

We trained two observers to take anthropometric measures according to procedures given
in the United Nations guide: "How to Weigh and Measure Children" [13]. Weight was measured to the nearest 10 g using a Tanita 1582 digital weighing scale,
which was quality controlled every morning using standard weights and the readings
plotted on a calibration chart. For children below 24 months, length was taken using
a wooden length board to the nearest 1 mm using a standard UNICEF design [14]. Height, which was taken among children 24 months or more, was measured using a wooden
stadiometer to the nearest 1 mm using a mounted tape measure according to the UNICEF
design. MUAC was measured on the left arm of the child using a tape to the nearest
2 mm using a dedicated insertion tape (Teaching Aid and Low Cost (TALC) St Albans,
UK).

We established the inter-observer variation between the two observers. Each observer
took MUAC, weight and height/length measures among children aged between 3 months
and 5 years admitted to the paediatric ward. The two sets of measures were taken within
30 minutes and were blinded from the other observer.

Ethical consideration

The study was approved by the Kenyan National Scientific and Ethical Review Committees
(SCC 1418). Verbal consent was given by the caregiver of the child during the second
measurement.

Statistical methods

For the inter-observer study, the required sample size was determined using the sample
size design for reliability studies [15,16]. This method calculates sample sizes for studies where the intra class correlation
(ICC) is used as a measure of reliability.

For the repeated measures study, we calculated the sample size for paired studies
using the formula described by Fleiss L. J et al [17], which is dependent on the difference between means and the within-group variability
of individual measurements. To establish mean and standard deviation values for this
population, we used historical MUAC data of hospitalised children from birth to 5
years collected between the years 2000 to 2005. We assumed that an arbitrary difference
of 0.5 cm for MUAC would be clinically relevant.

Calculated sample sizes were n = 53 for the inter-observer study, and n = 285 for
the repeated measures study each giving a 90% power of rejecting the null hypothesis
of no difference at the 0.05 level of significance. In order to allow for drop out
of children from the study, we rounded up these numbers to n = 60 and n = 300 children
for the inter-observer and repeated measures study respectively.

Anthropometric Z score calculations for weight-for-length (WFLz), weight-for-age (WFAz),
height-for-age (HFAz) and MUAC-for-age (MUACz) were computed using the 2006 WHO standards
[2]. Statistical analysis was carried out using STATA version 11.0 (STATA Corp, College
Station, Texas).

Rehydration solutions (ORS and ReSoMal), and the starter milk formula (F-75) used
for stabilization of severely malnourished children provide hardly any energy and
little protein, making deposition of lean or fat tissue negligible and unlikely to
influence measures. Thus, we assumed that changes in weight and MUAC among acutely
ill hospitalized children with signs of dehydration over 48 hours were predominantly
due to changes in body water rather than tissue deposition. Absolute, percentage and
Z score changes in MUAC and WFLz of the children between the first and the second
measurements were calculated. Linear regression, adjusted for age and sex was used
to quantify changes associated with rehydration.

Four categories of rehydration were defined: less than 0%, 0-4.9%, 5-9.9%, and 10%
or more change in body weight. Changes in MUAC and WFLz for children in these categories
of dehydration were calculated. Three categories of wasting were defined as severe,
moderate and none using MUAC cut offs of < 115 mm, 115 to 124 mm, and 125 mm or more;
and using WFLz by <-3, -3 to -2.01, and -2.01 or more. The proportion of children
whose anthropometric nutritional classification changed after 48 hours was calculated
with 95% confidence intervals (CI).

Repeated measures study

Between February and August 2009, 382 eligible children were admitted. Forty one had
missing information including missing second measures (n = 36) and 5 were missing
Z score values for the 1st or 2nd measurement. Eight children died before the 2nd measure and another eight children were hospitalized for less than 2 days. Thus, data
on 325 children (61% male) were available for analysis; they had a median age of 11
months (IQR 8 to 18 months).

Of the 325 participants, 261 (80%) had a history of diarrhoea. One hundred and eighty
five (57%) had multiple signs of dehydration: 30% had 2 signs, 16% had 3 signs, 5%
had 4 signs and 6% experienced 5 or more signs at admission (Table 1). Out of the 325 participants, 37 (11%) had pneumonia, 10 (3.1%) had malaria parasitemia
and 9 (2.8%) had a positive HIV antibody test.

Table 1. Frequency of signs of dehydration at admission among the 325 study participants

In linear regression models, adjusted for age and sex, a one percent (1%) change in
weight, was associated with a 0.40 mm (95% CI of 0.30 to 0.44 mm, P < 0.001) change
in MUAC, 0.035z (95% CI 0.027 to 0.04z, P < 0.001) change in MUACz and a 0.115z (95%
CI of 0.11 to 0.12z, P < 0.001) change in WFLz. In all the models, age had no significant
effect; however, there was an effect of sex. There was no evidence of interaction
between sex and percent weight gain thus adjusted estimates were not gender stratified
in Table 2. Results did not significantly differ when we repeated the analysis after excluding
the 81 children who lost weight during the period studied.

Participants with more than 10% gain in body weight following rehydration, suggesting
severe dehydration had been present, had a mean change of +1.4 WFLz and +3.6 mm MUAC.
The percent changes on MUAC and WFLz across the different categories of dehydration
and their 95% CIs are presented in Figure 1. WFLz had much greater percentage changes, including a 20% change among the most
severely dehydrated compared to 6% change by MUACz and 3% change in absolute MUAC.

Figure 1.Percentage change in anthropometry for different categories of percent weight change
measured after 48 hours.

For analysis of changes in nutritional classification, children were initially included
irrespective of whether they gained or lost weight, and if they were 6 to 59 months
old (n = 292), since MUAC Cut-off values are currently undefined below this age group.
SAM at admission was more commonly identified by WFLz: 71 (24%) children classified
as severely malnourished by WFLz at admission compared with 48 (16%) children classified
as SAM by MUAC (P < 0.001). Of the 71 children with WFLz<-3, 15 (21%) were not severely
malnourished after rehydration. Of the 48 children with MUAC <115 mm, 9 (19%) were
not severely malnourished after rehydration. We repeated the analysis excluding the
patients who lost weight (n = 218). The proportions misclassified as having severe
malnutrition were increased to 32% and 23% for WFLz and MUAC respectively (Table 3).

Table 3. Potential misclassification in acute malnutrition among dehydrated children

For children classified as moderately malnourished by WFLz <-2, 21% were not moderately
wasted after rehydration whereas for children classified as moderately malnourished
by MUAC <125 mm, 7% were not moderately malnourished after rehydration (Table 3). After excluding those who lost weight, the proportion of admissions who were classified
as moderately malnourished changed to -29% for WFLz and +5% for MUAC.

Discussion

We have shown that among children admitted to a rural Kenyan district hospital; both
MUAC and WFLz were altered by rehydration. Among children who were rehydrated by 10%
or more of their admission body weight, the mean change in MUAC was 3.6 mm and in
WFLz was 1.4 z scores. We also found that amongst all children with signs of dehydration,
approximately one in five children who were classified as severely malnourished at
admission by either MUAC or WFLz were classified as non-severely malnourished after
48 hours. Amongst those who gained weight during the 48 hours, approximately one in
three became non-severe using WFLz compared to one in four using MUAC.

Since MUAC decreased in children who lost weight and increased proportionately with
the degree of rehydration among those who gained weight over a short period of time,
we believe that these changes were mostly due to changes in hydration.

There is a paucity of published literature describing changes on diagnostic criteria
for SAM among acutely ill hospitalised patients and none has previously reported a
repeated measures approach among children. In a study of adults with acute gastroenteritis,
anthropometric measures at admission and at 4 weeks post discharge indicated a significant
change in both weight and MUAC [18]. Similar to our findings, the authors concluded that the anthropometric changes observed
were explained by dehydration and not a change in nutritional status.

Our findings have important implications for the identification and management of
individual children with severe malnutrition and for estimations of the prevalence
of SAM among hospitalized children. They indicate that such studies may overestimate
the true prevalence of SAM and may potentially confound associations if dehydration
is also associated with the outcome studied. Since many deaths occur early in admission
[19] this is not easily resolved by using later measurements.

A recent study among severely wasted children (6 to 36 months) with cholera in Bangladesh
(mean admission WFLz -3.09 and MUAC 11.3 cm) [20] reported an average weight gain of approximately 11% at 72 hours post admission.
Anthropometric changes during this period were not evaluated. However, if our findings
are generalisable, then the 11% weight gain observed in that study would equate to
an increase of ~1.5z scores in WFLz after hydration. Many of the children may not
have fulfilled the WHO criteria for severe acute malnutrition at admission had they
not been dehydrated.

Our findings may reflect the hospital setting and may differ in a village or community
context where both the severity of illness and access to services vary. It is unknown
to what extent children with poor fluid intake and ongoing losses might become more
dehydrated during a long walk to access clinic services.

In our study, a quarter of the children lost weight suggesting further water loss
over the observation period. This did not alter our models for percentage change in
anthropometric indices. However, when these children were excluded, the proportion
who changed nutritional status classification was markedly increased. The difference
was especially evident for moderate malnutrition assessed by WFLz compared to MUAC.
It is recognised that signs of dehydration, including sunken eyes and delayed skin
pinch which were the most common signs in our study, may be unreliable indicators
in malnourished children [21]. It is therefore possible that dehydration could be over-diagnosed among malnourished
children. This study was not designed to discover whether this was due to children
not taking the prescribed amount of fluid, or whether strategies for rehydration were
effective.

A strength of this study was in assessing the inter-observer reliability of the two
observers before they were involved in data collection thus increasing the trustworthiness
of the results. It is notable that for inter-observer reliability, the lowest ICC
estimate was for the WFLz measurements. One limitation of this study is that we used
a 2 mm scale MUAC tape instead of a 1 mm graduated tape, which limited the precision
of absolute MUAC changes. The use of percentage weight change as a measure of hydration
may also be a limiting factor as food, drinks and passing stool or urine shortly before
measurement may also have altered weight. More precise estimation of hydration including
isotope dilution or bioelectrical impedance methods could be used in future.

Conclusions

We have shown that overall; MUAC is less affected by dehydration than WFLz. However,
changes in classification of severe acute malnutrition following rehydration were
similar using the two measures. We recommend assessment of ill children by MUAC because
it is affected less by dehydration. Dehydrated children who are classified as severely
malnourished should be managed according to protocols specific to malnutrition, including
F-75 milk and antimicrobials in addition recommended rehydration fluids and electrolytes,
and their anthropometry re-assessed after rehydration. Those who are then found to
be only moderately acutely malnourished, and who have regained appetite may then enter
a supplementary feeding programme in order to focus inpatient therapeutic resources
on children who are most at risk.

Competing interests

The authors declare that they have no competing interests.

Authors' contributions

MM designed the study and undertook training and supervision of the study activities,
data management, analysis and interpretation of the results and writing the first
draft of the manuscript. JB and AP conceived the study, participated in study design
and provided overall supervision, advice and expertise on the study. GF provided statistical
support and advice on design, analysis and interpretation. All authors were involved
in writing, have read and approved the final manuscript.

Authors' information

MM is a third year PhD student in nutrition epidemiology at the London School of Hygiene
and Tropical Medicine, London. This paper forms part of her overall PhD thesis on
the usefulness of MUAC among rural community children. GF is the lead statistician
at the KEMRI-Wellcome Trust Research Programme, Kilifi, Kenya and has been in post
since October 2003. He's interested in wide scale public health interventions. AP
and JB jointly supervise MM in all aspects of her work. AP is Head of the MRC International
Nutrition Group at LSHTM and MRC Keneba, The Gambia, and specialises in maternal and
child nutrition in sub-Saharan Africa. JB is a welcome Trust Intermediate Clinical
Research Fellow. His research focuses on interventions and the basic mechanisms involved
in the relationship between malnutrition and infection in children so as to improve
outcomes in malnourished children.

Acknowledgements

The author would like to thank Amos Kazungu and Patricia Shali for data collection
and entry, the late Dr Ali Mathenge who until his untimely death was a co-investigator,
Ministry of Health-Kenya, Kenya Medical Research Institute; Centre for Geographic
Medicine-Coast for their supporting and housing this study, and the study participants.
This work was supported by the Wellcome Trust with a strategic award from (084538)
(MM) and personal fellowship (083576) (JAB). It is published with the permission of
the Director, KEMRI.

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